1. Field of the Invention
This invention relates to a tilt type steering apparatus for a vehicle.
2. Related Background Art
There is known a height adjusting apparatus for a steering wheel called the tilt type steering apparatus adapted to be capable of changing the height of a steering wheel in conformity with the constitution, driving posture or the like of a driver. As such a tilt type steering apparatus, there is known one described, for example, in Japanese Utility Model Publication No. 2-34145.
The tilt type steering apparatus described in this publication is called the swing type and is constructed as shown in FIGS. 5 to 8 of the accompanying drawings. A steering column 2 formed into a cylindrical shape to insert a steering shaft 1 thereinto is bisected into a fore steering column 3 and a rear steering column 4. These two steering columns 3 and 4 are connected together by a support bracket 5 fixedly supported on a vehicle body. The rear steering column 4 is pivotally movable about pivot pins 6 and 6 provided coaxially with each other on the support bracket 5.
These pivot pins 6 and 6 are made into a bolt-like shape and have pillar portions 24 and 24 formed between large-diametered heads 22, 22 formed on the outer end portions thereof and externally threaded portions 23, 23 formed on the tip end portions thereof. The outer diameter of these pillar portions 24, 24 is larger than the outer diameter of the externally threaded portions 23, 23 and is smaller than the outer diameter of the heads 22, 22. The pivot pins 6, 6 are such that with the externally threaded portions 23, 23 threadably engaged with and fastened in threaded holes 25, 25 formed in the rear steering column 4, the pillar portions 24, 24 are positioned in circular holes 26, 26 formed in the support bracket 5. Accordingly, the rear steering column 4 becomes pivotally movable about the pivot pins 6, 6.
A restraining mechanism engageable by a tilt lever 7 pivotally movable about the pins 6, 6 is provided between the support bracket 5 and the rear steering column 4. Describing an example of this restraining mechanism in detail, one end of the rear steering column 4 is pivotally supported on the support bracket 5 by the pivot pins 6, 6 provided on the support bracket 5 fixed to a vehicle body on the underside or the like of a dashboard 8, and also a first engagement member 9 is fixed to the underside of the rear steering column 4. The underside of this first engagement member 9 is formed as an arcuately concave surface centering around the pivot pins 6, 6 and first engagement teeth 10 are formed on this underside.
On the other hand, one end (the left end as viewed in FIGS. 6 and 8) of a second engagement member 12 engageable with the engagement member 9 with the pivotal movement of the tilt lever 7 is pivotally supported on a lateral shaft 11 provided on the support bracket 5. Second engagement teeth 13 engageable with the first engagement teeth 10 formed on the underside of the first engagement member 9 are formed on the upper edge of the other end portion (the upper edge of the right end portion as viewed in FIG. 6) of the second engagement member 12. A roller 15 is supported on a shaft 14 having its end portion coupled to the lower end portion of the tilt lever 7 having its intermediate portion pivotally supported on the pivot pins 6, 6, and the upper surface of this roller 15 bears against the underside of the second engagement member 12. Further, a pin 18 protruding from the side of the second engagement member 12 is engaged with an inclined slot 17 formed in a rockable plate 16 fixed to the tilt lever 7.
With the construction as described above, when the tilt lever 7 is pivotally moved in a counter-clockwise direction as viewed in FIG. 6, the roller 15 retracts from below the other end portion (the right end portion as viewed in FIG. 6) of the second engagement member 12 and at the same time, the other end portion of the second engagement member 12 is downwardly displaced on the basis of the engagement between the inclined slot 17 and the pin 18. As a result, the engagement between the second engagement teeth 13 formed on the upper surface of the other end portion of the second engagement member 12 and the first engagement teeth 10 on the underside of the first engagement member 9 fixed to the underside of the rear steering column 4 is released (within such a range that a pin 19 projectedly provided on the side of the rear steering column 4 can be displaced inside an arcuate slot 20 formed in the support bracket 5) and the rear steering column 4 becomes pivotally movable about the pivot pins 6, 6. On the basis of this pivotal movement, the height position of a steering wheel fixed to the end portion of the steering shaft 1 inserted in the rear steering column 4 becomes adjustable.
When the height position of the steering wheel is adjusted in this manner, the tilt lever 7 is pivotally moved in a clockwise direction as viewed in FIG. 6. With this pivotal movement, the roller 15 comes into below the other end portion of the second engagement member 12 and pushes up the other end portion of this second engagement member 12, thereby bringing the second engagement teeth 13 formed on the upper surface of this other end portion into engagement with the first engagement teeth 10 formed on the underside of the first engagement member 9 fixed to the underside of the rear steering column 4. As a result, the rear steering column 4 is prevented from rotating about the pivot pins 6, 6 and holds the steering wheel at its adjusted height position. In this state, a resilient force which tends to pivotally move the tilt lever 7 in the clockwise direction as viewed in FIG. 6 is imparted to the tilt lever 7 by a tension spring 21 and therefore, it does not happen that the roller 15 inadvertently retracts from below the second engagement member 12.
(i) However, in the case of a pivotally supporting apparatus incorporated in the prior-art tilt type steering apparatus constructed and used as described above and pivotally supporting the fore end portion of the rear steering column 4, the assembling work has been cumbersome and the efficiency of the work of manufacturing the tilt type steering apparatus has been bad. That is, in the case of the prior-art apparatus, the work of bringing the externally threaded portions 23, 23 of the pivot pins 6, 6 into threadable engagement with threaded holes 25, 25 formed in the right and left sides of the rear steering column 4 and fastening them becomes necessary. This threadably engaging and fastening work need be done with a predetermined tightening torque to prevent the pivot pins 6, 6 from being loosened and coming off or from being tightened too much to thereby damage the threads, and is cumbersome.
In contrast, Japanese Patent Application No. 5-230026, as shown in FIG. 9 of the accompanying drawings, describes a structure in which a rear steering column 4a is pivotally supported on a support bracket 5a by pivot pins 6a, 6a having large-diametered portions 27, 27 and small-diametered portions 28, 28 connected together by stepped portions 29, 29. In this structure, the large-diametered portions 27, 27 are fitted in and fixed to circular holes 31, 31 formed in the support bracket 5a and reinforcing plates 30, 30 and also, the small-diametered portions 28, 28 are inserted in cylindrical sleeves 32, 32 supported on both side walls of the rear steering column 4a. Portions of the reinforcing plates 30, 30 are caulked diametrally inwardly of the circular holes 31, 31 to thereby achieve the anti-slippage of the pivot pins 6a, 6a.
In the case of the structure as shown in FIG. 9, the work of pressing or inserting the pivot pins 6a, 6a into the circular holes 31, 31 and the sleeves 32, 32 is easy, but the work of caulking portions of the reinforcing plates 30, 30 to prevent the slippage of the pivot pins 6a, 6a is cumbersome. Particularly, portions of the pair of reinforcing plates 30, 30 provided with the hollow tubular rear steering column 4a interposed therebetween are caulked and therefore, when the rigidity of the rear steering column 4a is insufficient, it is necessary to achieve the prevention of the deformation of this rear steering column 4a as by inserting a receiving mold into the rear steering column 4a. The work of putting such a receiving mold into and out of the rear steering column is cumbersome and it also makes the efficiency of the work of manufacturing the tilt type steering apparatus bad.
(ii) In the case of the prior-art tilt type steering apparatus shown in FIGS. 5 to 8, not only the assembling work has been cumbersome and the efficiency of the work of manufacturing the tilt type steering apparatus has been bad, but also the width dimension thereof has been large and therefore the space for installation has unavoidably been increased. That is, in the case of the prior-art apparatus, the work of bringing the externally threaded portions 23, 23 of the pivot pins 6, 6 into threadable engagement with the threaded holes 25, 25 formed in the right and left sides of the rear steering column 4 and fastening them becomes necessary. This threadably engaging and fastening work need be done with a predetermined tightening torque to prevent the pivot pins 6, 6 from being loosened and coming off or from being tightened too much to thereby damage the threads, and is cumbersome. Also, the heads 22, 22 of the pivot pins 6, 6 protrudes greatly from the outer side of the tilt lever 7 and therefore, the maximum width dimension of the tilt type steering apparatus becomes large. Therefore, in some cases, the design for enabling the apparatus to be installed in a limited space as under the dashboard becomes cumbersome.
(iii) In the case of the tilt type steering apparatus shown in FIGS. 5 to 8, it is necessary to provide a spring between the portion fixed to the support bracket 5 and the portion fixed to the rear steering column 4 and support the weight of the portion pivotally moved about lateral shafts 6, 6 with the rear steering column 4. The reason for this is as follows. The steering shaft 1 and the steering wheel are supported on the rear steering column 4 pivotally movable about the lateral shafts 6, 6. Therefore, the weight of the portion pivotally moved about the lateral shafts 6, 6 increases considerably. Accordingly, unless this weight is supported by a spring, as soon as the engagement of the aforedescribed restraining mechanism is released, the rear steering column 4 will downwardly rock forcibly to thereby hit a driver's foot or the like with force. Also, the driver will have to adjust the height position of the steering wheel while supporting this great weight, and the adjusting work becomes cumbersome.
As the spring for supporting the weight of the rear steering column 4, use is made of a tension spring or a compression coil spring. When a tension spring is used, this tension spring is disposed on the upper side of the steering column 2. In contrast, when a sufficient space cannot be secured on the upper side of the steering column 2, a compression coil spring is disposed on the lower side of the steering column 2. FIGS. 16 and 17 of the accompanying drawings show a prior-art structure in which for such a purpose, a compression coil spring 226 is disposed on the lower side of a steering column 202. In this structure, a rear steering shaft 223 and a fore steering shaft 222 are connected together by a universal joint 224.
The fore end portion (the left end portion as viewed in FIG. 16) of the compression coil spring 226 resiliently bears against the rear side (the left side as viewed in FIG. 16) of a fixed side receiving piece 227 secured to a portion of a support bracket 205 and downwardly protruding from the fore end portion (the left end portion as viewed in FIG. 16) of the support bracket 205. A bent-up piece 231 is bent up on the rear side of the fixed side receiving piece 227 at a right angle with respect to this rear side. The fore end portion of the compression coil spring 226 is fitted on the bent-up piece 231. The rear end portion (the right end portion as viewed in FIG. 16) of the compression coil spring 226 resiliently bears against the fore side (the left side as viewed in FIG. 16) of a pivotal movement side receiving piece 230 secured to a pivotally movable bracket 229 constituting a rear steering column 204a with a column tube 228 and downwardly protruding from the fore end portion (the left end portion as viewed in FIG. 16) of the pivotally movable bracket 229. A circular concave hole 232 is formed in the fore side of the pivotal movement side receiving piece 230 in a direction perpendicular to this fore side. The rear end portion of the compression coil spring 226 is fitted in the concave hole 232. By the compression coil spring 226 being assembled in this manner, this compression coil spring 226 resiliently stretches between the fixed side receiving piece 227 and the pivotal movement side receiving piece 230 and supports the weight of the portion pivotally moved about the lateral shafts 206, 206 with the rear steering column 204a.
In the case of such prior-art structure shown in FIGS. 16 and 17, when the rear steering column 204a is in its neutral state (a state in which the center axis of the fore steering column 203 and the center axis of the rear steering column 204a are made coincident with each other and the height of the steering wheel is in an intermediate position), the center axis of the compression coil spring 226 lies on a straight line from its fore end to its rear end. In other words, the center of the bent-up piece 231 and the center of the concave hole 232 lie on a straight line, and the center axis of the fore end portion of the compression coil spring 226 and the center axis of the rear end portion of this compression coil spring 226 coincide with each other. When from such a neutral state, the rear steering column 204a is pivotally moved in a counter-clockwise direction to elevate the height position of the steering wheel, the compression coil spring 226 becomes curved in a direction for the underside thereof to become arcuately convex as shown in FIG. 18 of the accompanying drawings. In contrast, when the rear steering column 204a is pivotally moved in a clockwise direction to lower the height position of the steering wheel, the compression coil spring 226 becomes curved in a direction for the upper side thereof to become arcuately convex as shown in FIG. 19 of the accompanying drawings. A structure using the compression coil spring 226 which becomes straight in the neutral position in this manner to support the weight of the rear steering column 204a is described, for example, in Japanese Patent Application Laid-Open No. 1-127453.
In the structure shown in FIGS. 16 to 19, the structure of a restraining mechanism provided between the portion fixed to the rear steering column 204a and the portion fixed to the fore steering column 203 somewhat differs from the structure shown in FIGS. 5 to 8. That is, in the structure shown in FIGS. 16 to 19, a first engagement member 209a having first engagement teeth 210a which are straight in the form of a rack formed on the underside thereof is fixed to the underside of a support bracket 205 fixed to the rear end portion of the fore steering column 203. Also, the rear end portion of a second engagement member 212a having second engagement teeth 213a which also are straight in the form of a rack formed on the upper surface of the fore end portion thereof is pivotally supported on the underside of the fore end portion of the rear steering column 204a via a shaft 211a. The first and second engagement teeth 210a and 213a are engageable with each other by a tilt lever, not shown. Such a restraining mechanism is not an essential portion of FIGS. 16-19, but its action itself is similar to that of the structure shown in FIGS. 5 to 8. Further, more specific structure of the restraining mechanism shown in FIGS. 16 to 19 is described in detail in Japanese Patent Application No. 6-123907 and therefore need not be described in detail herein.
In the case of the prior-art tilt type steering apparatus constructed and used as described above, the compression coil spring 226 produces unusual sound with the pivotal movement of the rear steering column 204a. That is, when the directions of forces applied from the opposite ends of the compression coil spring 226 are continuously changed while a force in a compressing direction is applied to the compression coil spring 226, the compression coil spring 226 vibrates at the moment when the neutral position is cleared. For example, when the rear steering column 204a is changed from the state shown in FIG. 18 to the state shown in FIG. 19 via the state shown in FIG. 16, the direction of curve of the compression coil spring 226 suddenly changes at the moment when the neutral position shown in FIG. 16 is passed, and this compression coil spring 226 vibrates. On the basis of this vibration, the compression coil spring 226 produces unusual sound which gives an unpleasant feeling to a crew such as a driver. Of course, such unusual sound is also produced when the rear steering column is changed from the state shown in FIG. 19 to the state shown in FIG. 18 via the state shown in FIG. 16.
In order to prevent the production of such unpleasant unusual sound, a member having a damping property such as a rubber tube has heretofore been put over the compression coil spring 226 or the end surface of the compression coil spring 226 and the inner peripheral side of the coil portion have heretofore been guided by a member made of synthetic resin. However, such prior-art structure requires discrete parts for preventing the production of unusual sound, which is the cause of the increased manufacturing costs of the tilt type steering apparatus.
(iv) In the case of the prior-art tilt type steering apparatus shown in FIGS. 5 to 8, it is difficult to both reduce costs and improve a feeling of operation. That is, to prevent the backlash of the steering wheel with the height position of the steering wheel fixed, it is necessary for the fixed side meshing teeth 10 and the displacement side meshing teeth 13 to mesh with each other reliably without any backlash (deeply). For this purpose, it is necessary that the directions of the meshing teeth 10 and 13 be made coincident with each other. If the directions of these meshing teeth 10 and 13 deviate from each other, the meshing engagement between these meshing teeth 10 and 13 will become unreliable (the meshing teeth 10 and 13 will mesh with each other only shallowly) even if the other end portion of the engagement member 12 is brought close to the restraining member 9, and this is liable to become the cause of the backlash of the steering wheel. Also, a feeling of moderation will become null as to the pivotal movement of the tilt lever 7 and this becomes the cause of a feeling of physical disorder given to the operator.
On the other hand, a plurality of members (in the case of the structure of FIGS. 6 to 8, the rear steering column 4, the lateral shafts 6, 6, the support bracket 5, and the lateral shaft 11) are present between the restraining member 9 provided with the fixed side meshing teeth 10 and the engagement member 12 provided with the displacement side meshing teeth 13. Therefore, the directions of the meshing teeth 10 and 13 are liable to deviate from each other on the basis of the shapes and dimensional errors of these members 4, 6, 5 and 11. In other words, to make the directions of the meshing teeth 10 and 13 coincident with each other, it is necessary to regulate the shapes and dimensional accuracy of these members 4, 6, 5 and 11 considerably strictly. It becomes the cause of the increased manufacturing costs of the members and accordingly the increased manufacturing costs of the tilt type steering apparatus to regulate the shapes and dimensional accuracy of the plurality of members 4, 6, 5 and 11 thus strictly, and this is not preferable.